1. Field of the Invention
The present invention relates to a technology for effectively utilizing a band of a network formed by SDH transmission apparatuses. Especially, the present invention relates to a technology for effectively utilizing a band of a network formed by SDH transmission apparatuses to which switch apparatuses having a link aggregation function are connected.
2. Description of the Related Art
In recent years, there are many cases where a link aggregation function is implemented in layer 2 apparatuses (a switch apparatus is taken as an example of the layer 2 apparatus in the following description) for performing processes on frames of the Ethernet and the like. The link aggregation function is a function, that is defined in IEEE802.3ad, for bundling plural links so as to handle the links as one link.
For efficiently transmitting traffic of signals transmitted and received between the switch apparatuses, an upper layer signal of the Ethernet and the like is accommodated in a lower layer signal such as the SDH (Synchronous Digital Hierarchy) signal to be transmitted. Therefore, a configuration in which the switch apparatuses are connected to the SDH transmission apparatuses that forms the SDH network is adopted. By the way, although there is a case where SDH is called SONET, SDH is used as a term including the meaning of SONET in the following.
FIG. 1 shows an example of a configuration of a conventional SDH transmission apparatus. As shown in the figure, the SDH transmission apparatus includes a low-speed part 1 for receiving a signal of the Ethernet and the like and converting the signal into an SDH signal, a multiplexing-demultiplexing conversion part 2 for performing signal multiplexing-demultiplexing, cross-connection and the like, and high-speed parts 3 for performing input/output of the SDH signal. The multiplexing-demultiplexing conversion part 2 includes a parallel/serial conversion circuit 21 for performing parallel/serial conversion for signals, a cross-connect circuit 22 for performing cross-connection, and a cross-connect information setting circuit 23 for setting the cross-connect circuit 22.
In addition, the SDH transmission apparatus includes a clock supply circuit 4, a main signal switching circuit/control monitor circuit 5, an alarm collection/output circuit 6. As shown in FIG. 2, the switch apparatus is connected to the low-speed part 1. In addition, by connecting plural SDH transmission apparatuses via the high-speed parts, a ring structured SDH network can be constructed, for example.
The link aggregation function in the switch apparatus provides high-speed communications by bundling plural ports as one link. Therefore, when a communication failure occurs in a particular port in the plural ports, the switch apparatus is set so as to keep the communication by using remaining ports.
Therefore, in the configuration in which the switch apparatus is connected to the SDH transmission apparatus that forms the SDH network, there is a following problem.
FIG. 3 is a figure showing a configuration in which a switch apparatus 11 and a switch apparatus 31 are connected to an SDH network including an SDH transmission apparatus 10 and an SDH transmission apparatus 30, so that communication is performed between the switch apparatuses 11 and 31 via the SDH transmission apparatuses 10 and 30. As shown in FIG. 3, the SDH transmission apparatus 10 includes Gigabit Ethernet termination parts 12 and 13 (shown as “GbE”) as the low-speed parts. The SDH transmission apparatus 30 includes Gigabit Ethernet termination parts 32 and 33 as the low-speed parts.
In the example shown in FIG. 3, a port A is connected to the Gigabit Ethernet termination part 12, and a port B is connected to the Gigabit Ethernet termination part 13 between the switch apparatus 11 and the SDH transmission apparatus 10. The ports and the Gigabit Ethernet termination parts are similarly connected between the switch apparatus 31 and the SDH transmission apparatus 30. In addition, between the switch apparatus 11 and the switch apparatus 31, a link 1 for connecting between the port A and the port C, and a link 2 for connecting between the port B and the port D are formed. Traffic data of X Mbps are transmitted on the link 1, and traffic data of Y Mbps are transmitted on the link 2.
By the link aggregation function of the of (X+Y) Mbps. In a lower layer level between the SDH transmission apparatuses 10 and 30, the link 1 and the link 2 are accommodated in separate paths. It is assumed that traffic of the link 1 is transmitted on a path 1, and traffic of the link 2 is transmitted on a path 2. In the present specification, “path” may be called “transmission line”.
From the normal state shown in FIG. 3, it is assumed that a failure occurs between the port B of the switch 11 and the Gigabit Ethernet termination part 13. That is, for example, it is assumed that a failure of the port B, a line failure between the port B and the Gigabit Ethernet termination part 13, or the like occurs. Then, settings of the switch apparatuses 11 and 31 are changed to maintain the traffic of (X+Y) Mbps regarded as one link only by using the link 1.
Therefore, as shown in FIG. 4, the traffic that has been flowing through the path 2 is changed to flow through the path 1. That is, although each of the path 1 and path 2 between the SDH transmission apparatuses 10 and 30 normally uses a band corresponding to X Mbps or Y Mbps, it is necessary to provide each path with a band of (X+Y) Mbps against the above-mentioned failure. That is, it is necessary to prepare a band of 2 (X+Y) Mbps between the SDH transmission apparatuses. By the way, assuming such a situation, a margin of band is also provided between the switch apparatus and the SDH transmission apparatus.
As mentioned above, according to the conventional technology, there is a problem in that it is necessary to provide a redundant path band in between the SDH transmission apparatuses against the above-mentioned failure. A patent document: Japanese Laid-Open Patent Application No. 10-117175 relates to the SDH transmission apparatus.